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Re: [dm-devel] multipath and san fabric



Yep - Ed caught my typo....  :)

-- james

Philip R. Auld wrote:
Rumor has it that on Mon, Nov 13, 2006 at 02:39:08PM -0500 Edward Goggin said:
You may want to also cross connect across the 2 target
controllers (A,B) in case 2.  Doing so provides more
redundancy for asymmetric arrays and better resource
utilization in case of a failure of either an HBA or
target controller which would otherwise prevent
utilization of the other HBA or target controller
for that LU when load sharing I/O across multiple
paths.

So the I_T nexus's for the 4 paths are:

	HBA1_TargetPort1
	HBA1_TargetPort3
	HBA2_TargetPort2
	HBA2_TargetPort4


That's exactly what James's example 2 describes. It's just typo'd in the DM paths list.


-----Original Message-----
From: dm-devel-bounces redhat com [mailto:dm-devel-bounces redhat com] On Behalf Of James Smart
Sent: Monday, November 13, 2006 2:18 PM
To: jslittl hendricks org; device-mapper development
Subject: Re: [dm-devel] multipath and san fabric

If the hba's are on different fabrics - why would you ever put an hba
that is not in the fabric in a zone in that fabric ? (e.g. your second
option makes no sense).

If you are stating that the 2hba's are on different fabrics (and in zones within those fabric) - but they are seeing the same Storage device on both fabrics - then the dm config (note: I'm not talking about zoning anymore) would have a path per I_T nexus. I state it this way to account for dual-ported controllers, which may appear as separate targets, may exist within the fabric.

Example 1:
Fabric A contains HBA1 and TargetPort1. Typically a zone would exist
     within Fabric A that contains these 2 ports.
Fabric B contains HBA2 and TargetPort2. Typically a zone would exist
     within Fabric B that contains these 2 ports.
The storage array contains 2 controllers with 1 port per controller, or is a single controller with 2 ports. Either way, the two ports are TargetPort1 and TargetPort2, are on the same array, and all storage
     can be seen from any port.
   --
   This would have 2 DM paths.
   The I_T nexus's are:
      HBA1_TargetPort1
      HBA2_TargetPort2

Example 2:
Fabric A contains HBA1, TargetPort1, and TargetPort3. Typically a zone
     would exist within Fabric A that contains these 3 ports.
Fabric B contains HBA2, TargetPort2, and TargetPort4. Typically a zone
     would exist within Fabric B that contains these 3 ports.
The storage array contains 2 controllers, with 2 ports per controller. Meaning TargetPort1 and TargetPort2 are on controller A, and TargetPort3 and TargetPort4 are on controller B. The ports are cross connected on the fabrics for redundancy. All storage can be seen from any port.
   --
   This would ahve 4 DM paths
   The I_T nexus's are:
      HBA1_TargetPort1
      HBA1_TargetPort2
      HBA2_TargetPort3
      HBA2_TargetPort4

-- james

John Little wrote:
Hi all

Admittedly this is not the correct forum for this question
but I have googled
this and the only people I have to ask around here are
people who won't touch
it because it is Linux.

My question is this: I'm using SLES10 with two emulex
hbas, one connected to
fabric a and one to fabric b. When zoning the switch for
the hbas do I put
in only one path to the fabric per hba or do I put in two,
one to each of the
separate fabrics?

Again I realize this is not exactly the correct forum but
since I couldn't
find an answer anywhere else I figured you guys would be the most knowledgeable. If there are some docs somewhere that you
could point me to I
would appreciate it.

John

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